Disk drives are an important data storage technology. Read-write heads are one of the crucial components of a disk drive, directly communicating with a disk surface containing the data storage medium. Read-write heads generate heat during write operations due to the large currents required for that operation. The inventors have discovered quality problems associated with thermal expansion, causing tip protrusion. A review of the relevant background will be made before discussing their discovery of the problem and their solutions.
FIG. 1A illustrates a typical prior art high capacity disk drive 10 including actuator arm 30 with voice coil 32, actuator axis 40, head arms 50–58 with head suspension assembly 60 placed among the disks.
FIG. 1B illustrates a typical prior art high capacity disk drive 10 with actuator 20 including actuator arm 30 with voice coil 32, actuator axis 40, head arms 50–56 and head suspension assemblies 60–66 with the disks removed.
FIG. 2A illustrates a head gimbal assembly including head suspension assembly 60 with head slider 100 containing the read-write head 200 of the prior art.
Since the 1980's, high capacity disk drives 10 have used voice coil actuators 20–66 to position their read-write heads over specific tracks. The heads are mounted on head sliders 100, which float a small distance off the disk drive surface when in operation. The flotation process is referred to as an air bearing. The air bearing is formed by the read-write heads 200, illustrated in FIG. 2A, and head slider 100, as illustrated in FIGS. 1A–2A. The flying height of the air bearing is very small, often about 100 Angstroms, or about 0.4 millionths of an inch, which is far smaller than a human hair.
Often there is one head per head slider for a given disk drive surface. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator.
Voice coil actuators are further composed of a fixed magnet actuator 20 interacting with a time varying electromagnetic field induced by voice coil 32 to provide a lever action via actuator axis 40. The lever action acts to move head gimbal assemblies 50-56, positioning head suspension assemblies 60-66, and their associated head sliders 100 containing read-write heads 200, over specific tracks with speed and accuracy. Actuator arms 30 are often considered to include voice coil 32, actuator axis 40, head gimbal assemblies 50–56 and head suspensions 60–66. An actuator arm 30 may have as few as a single head gimbal assembly 50. A single head gimbal assembly 52 may connect with two head suspensions 62 and 64, each with at least one head slider.
FIG. 2B illustrates the relationship between the principal axis 110 of an actuator arm 50 containing suspension 60, which in turn contains head slider 100, as found in the prior art.
FIG. 2C illustrates a simplified schematic of a disk drive controller 1000 of the prior art, which may be used to control a spin stand test unit.
Disk drive controller 1000 controls an analog read-write interface 220 communicating resistivity found in the spin valve within read-write head 200. Disk drive controller 1000 concurrently controls servo-controller 240 driving voice coil 32, of the voice coil actuator, to position read-write head 200 to access a rotating magnetic disk surface 12 of the prior art.
Analog read-write interface 220 frequently includes a channel interface 222 communicating with pre-amplifier 224. Channel interface 222 receives commands, from embedded disk controller 100, setting at least the read_bias and write_bias.
Various disk drive analog read-write interfaces 220 may employ either a read current bias or a read voltage bias. By way of example, the resistance of the read head is determined by measuring the voltage drop (V_rd) across the read differential signal pair (r+ and r−) based upon the read bias current setting read_bias, using Ohm's Law.
FIG. 2D illustrates a detailed view head suspension 60 of the prior art.
A prior art head suspension 60 includes suspension load beam 80 mechanically coupled via hinge 82 with extended base plate 84. Head suspension 60 further includes flexure 86, providing electrical interconnections of the read and write differential signal pairs 210, between the disk drive analog interface 220 and read-write head 200 (both in FIG. 2C).
The head gimbal assembly includes head slider 100 rigidly mounted on head suspension 60, with read-write head 200 electrically connected to flexure 86. Head slider 100 is mounted over the right portion of suspension load beam 80 so that read-write head 200 makes contact with flexure 86.
The hinge 82 includes a spring mechanism. Suspension load beam 80, hinge 82 and extended base plate 84 are all typically made from stainless steel. Flexure 86 is a flex printed circuit typically made using polyamide and copper traces.
What is needed are reliable head gimbal assemblies and actuators, which will minimize read-write head crashes by reliably maintaining the flying height, even as the flying height decreases and the data rates increase, to insure the quality of the disk drives in which they are used. The inventors know of no known discussion of the relationship between thermal pole tip protrusion to reliably maintaining the flying height.